Import most of Common.v, add a bit to PreCategory
Improve things; add symmetry and etransitivity
Improve the timers

Time     | File Name
------------------------
0m02.04s | Functor
0m00.18s | Common
0m00.18s | PreCategory
0m00.07s | Utf8
0m00.04s | Notations
0m00.04s | NotationsUtf8
------------------------
0m02.55s | Total
Add *.pyc to .gitignore
Add *.log to .gitignore
Add NaturalTransformation

After    | File Name             | Before
-------------------------------------------
0m06.50s | NaturalTransformation |   N/A
0m02.14s | Functor               | 0m02.11s
0m00.21s | Common                | 0m00.20s
0m00.18s | PreCategory           | 0m00.15s
0m00.06s | Utf8                  | 0m00.09s
0m00.06s | NotationsUtf8         | 0m00.05s
0m00.05s | Notations             | 0m00.06s
-------------------------------------------
0m09.20s | Total                 | 0m02.65s
Clean up Makefile